Metal pipe has been used buried below ground to carry oil, gasoline, petroleum products or harmful solvents. Steel or iron pipe has been used, but generally requires the use of several layers of resin coatings outside or polymeric tape wrapping materials to provide protection from the environment. Examples of patents relating to the application of two or more polymer coatings are U.S. Pat. Nos. 4,213,486 to Samour et al. and 3,420,277 to Ceintrey. However, steel pipe cannot be coiled nor easily bent for purposes of installation.
Copper pipe has been used for carrying these fluids below ground and also embedded in concrete walls and floors. Copper is more easily deformed than steel or iron pipe, and is desirably less subject to corrosion when buried because it tends to form a protective film with mixtures of oxide, basic carbonate and basic sulfate. Conventionally, bare copper piping used to supply fuel oil to oil burners has at least a 3/8 inch O.D. (outside diameter) and a 0.035 inch nominal and 0.032 inch minimum wall thickness.
Copper tubes, however, have disadvantages because they are subject to corrosive attack by acidic or basic conditions in the soil, which may exist naturally or be influenced by vegetation or fertilizers, or alkaline attack in the concrete. After time, leaks may form in a copper pipe permitting the fluid being carried therein to leach into the surrounding soil or structure. If the fluid is fuel oil or gasoline, nearby water and soil may be adversely affected. Further, local or national regulations of governmental agencies may require site clean-up if a fuel oil leak occurs, a potentially costly affair. Such a financial burden weighs particularly heavy on homeowners experiencing a leaky fuel oil conduit.
Several solutions have been attempted. Polymeric tape wrapped around bare copper pipe prior to installation can provide some protection. Bare pipe has also been encased in polypropylene sleeves prior to installation. These methods involve extensive labor to install, and pose the risk of incomplete barrier protection.
Plastic pipes of polyethylene or polyvinyl chloride have also been used. However, while offering resistance to chemical attack, plastic pipes have several shortcomings. They are, for example, generally slightly permeable to water and gas. Flexible plastic tubes have relatively low mechanical strength, making them less able to withstand mechanical stress and pressure in the system, which may make them collapse or burst. Rigid plastic pipes, such as rigid polyvinyl chloride (which may consist of the homopolymer, copolymer, or polymer blends), are insufficiently deformable to provide convenient installation.
U.S. Pat. No. 3,570,545 (Benteler) proposes a steel tube having a copper inner liner and plastic outer jacket, and U.S. Pat. No. 2,039,781 (Debenedetti) uses two concentric copper tubes with an intermediate rubber liner in an attempt to provide an improved conduit.
U.S. Pat. No. 4,216,802 (Bonnes et al.) provides a composite conduit for carrying corrosive fluids formed of a commercially standard sized copper tube to which is bonded with a hot melt adhesive a polyvinyl chloride coating of a thickness that must be tightly controlled to be 50% or more of the total radial wall thickness. The composite tube is said to be a standard outer diameter that may be used with the same conventional fittings as used for unitary metal or plastic tubes without having to skive away the outer plastic in order to provide a fluid-tight seal.
It is, therefore, an object of the invention to provide a coated metal pipe structure that may be disposed below ground to safely convey petroleum products or harmful solvents that is simple to fabricate and install, uses a minimal number of different components, has low manufactured cost, and that can be shipped and stored as a rolled coil, and which will resist attack by the fluid being conveyed and by acidic or alkaline conditions in the adjacent soil or concrete in which it is disposed.